Optical imaging is a promising alternative to imaging modalities such as X-rays, MRI, ultrasound, PET and the like and possesses advantages such as using non-ionizing radiation and being able to provide functional in addition to anatomical information.
It is well known from classical models, diffusion and transport equations and experimental measurements that time resolved methods such as Time Domain (TD) and Frequency Domain (FD) optical imaging can be exploited to recover optical properties of the medium by forward or inverse problems modeling (Hawrysz and Sevick-Muraca Neoplasia, Vol. 2 No. 5 pp 388-417, 2000). However, these calculations are time consuming and very sensitive to noise due to the number of free parameters required. These limitations are particularly felt in optical imaging.
Furthermore, the aforementioned calculations often assume that the volume sampled is homogeneous with regard to the optical properties of the underlying medium. This, of course, greatly reduces the spatial resolution of the determination of optical properties.
More direct approaches have been suggested to determine optical properties of turbid media using time domain. For example U.S. Pat. No. 5,386,827 describes a TD method to determine the absorption coefficient of a biological tissue based on the decay slope of the TPSF. However, this approach does not solve the problem of spatial resolution in the case where the medium is inhomogeneous with respect to its optical properties.
There is therefore a need for improved methods for determining the spatial distribution of optical properties in heterogeneous media.